Hello there....most common cause for missing periods is pregnancy unless ruled out....Termination of pregnancy is done upto 20weeks only for certain indications.... In a normal menstrual cycle, a balance between the hormones estrogen and progesterone regulates the buildup of the lining of the uterus (endometrium), which is shed during menstruation. If a hormone imbalance occurs, mentrual irregularities occurs.. Consult Gynecologist....